Process for the manufacture of rubber articles



Patented Nov. 13,1951

PROCESS FOR THE MANUFACTURE OF RUBBER ARTICLES Rebecca 0.Teston, Glenbrook, Conn., assignor to Eastern Rubber Specialties, South Norwalk, Conn, a corporation of Connecticut No Drawing. Application June 24, 1948,

Serial No. 35,051

1 Claim. 1 This invention relates to the manufacture of rubber articles from dispersions of latex through the coagulation of latex upon a form or mold. More particularly, this invention relates to an earlier invention set forth in my application Ser.

No. 721,448, filed January 10, 1947, for a process for the manufacture of rubber articles, now

Patent No. 2,482,075.

For a number of years it has been customary to manufacture rubber articles from latex by coating a solid form with a dispersion of latex and thereafter subjecting the dispersion of latex to the action of a coagulant. After treatment with the coagulant, the form is dipped intoa dispersion of latex with the coagulant acting on the dispersion of latex to build up the thickness of latex on the form. Thereafter, further dip.- pings in latex and coagulant may follow, depending upon the thickness of the final product that is desired. After the latex is vulcanized, the finished product is stripped off the form. As pointed out in my earlier application, much time and effort is expended in stripping thefinished articles from the forms, and frequently those finished articles are damaged in the process.

Another method used by the prior art for forming hollow rubber articles comprises applying to the form a coagulant, after which the form with the coagulant coating is placed in a dispersion of latex and the latex coagulated on the form and dried. While' advantages in speed and economy are claimed for this process, those skilled in the art have found that one of the most important features thereof is the facilitated stripping of the finished product brought about by the presence of the coagulant between the latex and the form.

It has been found, however, in the utilization of these processes that defective articles are frequently produced. This is due, I believe, to the fact that gases develop to maintain the latex spaced from the form. Where rubber dolls or the like are to be manufactured, it is of course readily understood that with the latex spaced from the form, the finished article will not have the detail of the form and frequently will, in fact, be quite misshapen. For this reason, these processes, the second of which is termed by the trade the Anode process, have not been found fully successful for the manufacture of dolls or other objects that are required to take on the fine detail of the forms on which they are made.

At this point it will be Well to indicate that an effort has been made to vent the offending gases through the utilization of a venting and vapor pervious material. This contribution to the art is fully set forth in the Newton Patent No. 1,924,214, and while the use of this contribution has perhaps helped somewhat, it is still difficult, if not impossible, to obtain consistently good finished products through the utilization of the processes set forth. This is particularly true of the manufacture of dolls and the like.

In my earlier application supra, I disclose the utilization of a lubricant, preferably wax, that is applied to the form in advance of the latex dip. It seems that this lubricant will adhere very closely to the form and without the forming of gas pockets between it and the form. In other words, the wax lubricant so closely adheres to the form that there is no possibility for any gas to form therebetween. In effect, the wax forms a non-venting gas impervious stratum whereas adapted for the manufacture of dolls or other similar articles in which considerable detail is imparted to the latex by close association thereof with the mold.

' In my earlier application, I utilize as the lubricant an aqueous dispersion of paraffin, an aqueous dispersion of micro-crystalline wax, and even solutions of parafiin or mutton tallow in carbon tetrachloride. While the process of my earlier application is extremely successful and yields articles far superior to those that may be obtained by prior art processes, I believe that I have now improved considerably the said earlier process and shall set forth this improvement in this application.

The basic improvement of this application resides in the utilization of a suspension of powdered wax as the lubricant dip to precede the dip into latex. Thus, I have found that by first dipping the form into a suspension of powdered wax, and then drying the resulting coating on the form, I obtain an evenly coated form with the powdered wax adhering so very closely to the form that no gas or air bubbles can form therebetween. Moreover, the form, when thereafter dipped into latex, will cause the latex to adhere to the form with no air or gas bubbles forming between the latex and the powdered wax. Thus, I obtain through my new process all the results that are inherent in my earlier application. However, my new process is superior to that of the earlier contribution, although falling within that contribution, for the reason that it is much more simple to maintain the suspension of wax than itis to maintain the emulsions of the prior art. Moreover, a suspension of powdered wax, especially in water, dries rapidly when applied to either a hot or cold form. Still further, I have found that the powdered wax will tend to melt during the drying or vulcanizing and drying of the finished latex product so as to greatly facilitate the stripping of .the latex product from the form.

In practicing my invention, I utilize an'inexpensive mold or form which may-be of glass, metal, ceramics, plastics, etc., all as those skilled in the art will fully appreciate. This form is first dipped into a suspension of a powdered waxy material, the waxy material being prefer- .ably stearic acid. I-referably, I use .a :Wetting agent and-a. fungicide, theactual preferred for- -mula for the suspension beingthen as follows: il'O'LO parts water, 3.5 parts stearicaoid, 2.0 parts wetting agent, and 0.05 part fungicide.

In preparing the suspension, water containing some of the wetting agent is slowly added to thepowdered stearic acid with the mixture stirred \until allthe stearic acid is in suspension. The resultingheavy suspension of stearicacid is then .stirred into the remainder of the water and the wetting agent. The fungicide is dissolved in water .and is stirred into the stearic acid suspension. Circulation of the suspension is necessary .at all times .in order to keep the powdered stearic acid in a uniform suspension. The fungicide .prevents the development of fungi in the suspen- .sion and is therefore preferably part of the composition.

When the form is removed from the suspension of stearic acid, it is dried and then dipped into the latex. Thereafter, the form is dipped into the coagulant and may be dipped again into latex and into coagulant with the dips repeated as many times as is necessary tobuild up the required thickness. I prefer the latex dip in advance of the coagulant dip as it seems to produce better results than are presently obtained by a reversal of the order.

The forms with the latex coag'ulated thereon are then dipped into leachingwaterand dried. Preferably, I utilize ire-vulcanized'latexand .the drying thereoi will complete the manufacture of the finished article. However, unvulcanized latex Particle.

article from the form is carried on immediately after the. dryingof the article or within a period :.of .time such that the form remains warm, the

stripping operation will be extremely simple. I

have foundzlahatthelatex articles will strip very vswiftlyaand easily from the form and without any damagethereto. "-Moreover, the finished article .will embody all-tthe necessary detail of the form suclrrequired by the art.

I believe that the considerable merit of my invention-and its relation to the prior art will now be understood.

1'. now claim:

The. processof forming hollow rubber articles thatcomprises dipping a form into a suspension of powdered stearic acid in water, drying the .form'so .as.'to.leave".thereon a film of powdered stearic acidlthat is. gas impervious and lubricating, said: film being extremely thin so as not to afiect appreciably the outer idetail of. the mold surfaces and: the resulting detail of the: hollow rubberzarticle, coagulating. on said film covered form a* coating of latex, drying the latex coating while-maintaining thesaid latex coating at a temperature at which the stearic acid film tends to melt and to become very slippery, and strip- .ping the" latex..-coating oil said form while the said stearic acid film is present between said mold. and article and isin said slippery condition.

*REBECCA O. TESTON.

:REEERENCES CITED "The following references are of record in the file of-this patent:

UN ITED, STATES PATENTS Number Name Date 1,876,229 Herzog -Sept. 6, 1932 1,887,190 Twiss Nov. 8; 1932 1924 214 Newton Aug". 29,1933 2,07 6,949 'Kirby Apr. 13, 1937 OTHER REFERENCES .Warth,. Chemistryand Technology of Waxes,

.1947, page308. 

